In my opinion, you should consider different focal lengths depending on the working space you have. If you're doing street photography in a crowded place, a 35mm would suit you, or maybe something wider. If you're shooting in a less crowded place, a 50mm is the way to go. If you're shooting a wedding, maybe you could have a 100mm for some nice bokeh. Of course you can always have a zoom lens, but those are just more expensive and don't have IQ as good as a prime lens.And from where I see it, if you consider both what you and I said, you can choose your lens for portrait. Of course I think that what you said is more important, but sometimes you might have to consider what I said as well.

Anyways, if what I said is ridiculous in any way, don't hesitate to criticize me (constructively obviously), I'll be more than glad to be corrected